132  Preserving  the  Color  of  Dried  Plants.  {^£&^m' 
Finally,  the  poison  ivy,  as  its  name  indicates,  possesses  an  acrid 
juice  that  is  intensely  irritating  to  the  skin  and  mucous  mem- 
branes. On  the  other  hand,  the  Virginia  creeper  is  harmless,  and 
may  be  handled  with  impunity. 
The  botanical  characters  of  these  two  plants  are  thus  seen  to  be 
markedly  different,  and  but  little  difficulty  is  presented  in  distin- 
guishing them. 
THE  USE  OF  OXALIC  ACID  IN  PRESERVING  THE  — 
COLOR  OF  DRIED  PLANTS. 
By  J.  Henry  Schroeder. 
The  importance  of  a  well-selected  herbarium  is  known  to  every 
botanist  of  the  present  day.  It  presents  to  him  the  most  important 
specimens  of  the  flora  so  far  as  known,  and  the  better  the  speci- 
mens are  preserved,  the  more  valuable  the  collection.  A  very  im- 
portant, if  not  the  most  important,  question  is,  how  to  preserve  the 
natural  color  of  the  foliage,  as  well  as  the  color  of  the  petals. 
No  doubt,  the  rapidity  with  which  the  plant  is  dried  greatly  in- 
fluences the  preservation  of  the  natural  color ;  but  in  the  course  of 
time  the  great  majority  will  fade,  while  others  acquire  different 
shades,  some  turn  black,  some  brown  and  various  other  colors. 
This  last  change  of  color  frequently  takes  place  while  the  plant  is 
bring  dried,  and  more  rarely  later  on. 
Not  only  the  leaves,  but  the  petals  of  most  flowers  change  in  the 
same  way,  thus  lowering  the  value  of  the  specimen  to  a  considerable 
extent. 
Nienhaus  published  in  the  Schweizerische  Wochenschrift  fur  Che- 
mie  und  Pharmacie1  his  experience  with  oxalic  acid  as  a  preserving 
agent  of  the  color  of  petals  of  dried  plants.  His  theory  was  that 
ammonia  in  the  air  caused  the  fading  of  the  color,  and  that  it  would 
be  neutralized  by  this  acid ;  therefore,  he  recommended  that  the 
plant  be  dried  between  filter-paper,  which  had  previously  been 
saturated  in  a  I  per  cent,  solution  of  the.  chemical,  and  then  dried. 
Nienhaus  experimented  with  the  petals  of  Papaver  Rhceas,  and  was 
very  successful.  According  to  some  American  writers,  who  have 
repeated  his  experiments,  the  results  were  entirely  negative.2 
1  Monatsblatt  des  deutschen  Apotheker  Vereins  von  New  York,  March,  1895 
(B.  I,  11). 
2  Bulletin  of  Pharmacy,  June  1895,  p.  269. 
